1. Field of the Invention
The present invention relates to a cleaning apparatus and a cleaning method for a wafer preferable for manufacturing a semiconductor device.
2. Description of the Related Art
Recently, in a manufacturing process of a semiconductor device, it is becoming essential to planarize a film or the like having been formed by that time by performing a CMP (Chemical Mechanical Polishing) processing before a photolithography, in order to secure an exposure margin for the photolithography. Here, a method of planarization by the CMP processing will be described with reference to FIG. 10. FIG. 10 is a schematic view showing an outline of a CMP apparatus.
The CMP apparatus is provided with a polishing table 51 on a surface of which a polishing pad 52 is affixed, a polishing head 54 holding a wafer 53, and a slurry supplying nozzle 55 supplying slurry (suspension containing a grain of abrasive) 56. Further, the CMP apparatus is provided with a dressing apparatus 57 dressing the polishing pad 52. The polishing table 51 and the polishing pad 52 are rotatable around their own axes.
In a CMP processing using the CMP apparatus with such a constitution, the slurry 56 is supplied from the slurry supplying nozzle 55 onto the polishing pad 52 while the polishing table 51 is being rotated, and the wafer 53 is pressed on the polishing pad 52 while the polishing head 54 is being rotated. As a consequence, the wafer 53 is polished by the polishing pad 52. To a portion of the polishing pad 52 which is squashed due to the wafer 53 being pressed on, a dressing is performed by the dressing apparatus 57 during rotation.
The CMP processing is performed as above, and the abrasive grain contained in the slurry, metal impurity, or the like remain on the wafer 53 after the CMP processing. Thus, a cleaning of the wafer 53 is required after the CMP processing. Here, a conventional cleaning method of a wafer will be described with reference to FIG. 11 and FIG. 12. FIG. 11 is a perspective view showing a conventional cleaning apparatus, while FIG. 12 is a front view showing the conventional cleaning apparatus.
The conventional cleaning apparatus is provided with two cylindrical brushes 63 contacting a front surface and a rear surface of the wafer 53, respectively. The brush 63 is made of synthetic resin and a plurality of projections are formed on a surface thereof. Additionally, a shaft 62 is inserted into the brush 63. In a cleaning using this apparatus, the brushes 63 and the wafer 53 are rotated while the two brushes 63 are made to contact the front surface and the rear surface of the wafer 53.
It is also carried out that a plurality of such cleaning apparatuses are provided to perform cleanings using different cleaning solutions. For example, after a cleaning is performed with an ammonia solution being supplied, another cleaning may be performed with a fluorinate acid being supplied. By this method, the abrasive grain is removed by the cleaning using the ammonia solution and the metal impurity is removed by the cleaning using the fluorinated acid.
By these methods, a sufficient cleaning is possible for a wafer with a diameter of 200 mm or less. However, when the cleaning is performed for a wafer with a diameter of about 300 mm according to the above-described method, numerous foreign objects 58 remain on an outer peripheral portion of the wafer 53 as shown in FIG. 13. This is considered because times during which a central portion and the peripheral portion of the wafer 53 contact the brush 63 are different. That is, in the peripheral portion, time during which the wafer is apart from the brush 63 is relatively long and a cleaning efficiency is deteriorated.
Thus, there is disclosed an art in which a brush having larger diameters in both ends is used to increase the cleaning efficiency in the outer peripheral portion (Patent Document 1).
However, using the brush having the larger diameters in the both ends is not practical. This is because a variation of the diameter of the brush must be adjusted in response to the diameter of the wafer. Moreover, since a direction and an amount of a warp of the wafer vary in response to a kind, a number, and a pattern and the like of films already formed, it is required to prepare more various brushes in order to correspond also thereto.
For example, in such a case as after a CMP processing for forming an element isolation region by STI (Shallow Trench Isolation), the wafer 53 is warped into a shape of a mound as shown in FIG. 14A. As a result, on the front surface of the wafer 53 the outer peripheral portion is hard to contact the brush 63. On the other hand, in such a case as after a CMP processing for forming a metal wiring, the wafer 53 warps into a shape of a bowl as shown in FIG. 14B. As a result, on the front surface of the wafer 53 the outer peripheral portion is easy to contact the brush 63, while on the rear surface the outer peripheral portion is hard to contact the brush 63. Therefore, unless brushes of a plurality of kinds are prepared for the same wafer, foreign objects on the front surface and the rear surface of the wafer 53 cannot be removed sufficiently. Additionally, not only the direction of the warp but also the amount of the warp varies in response to a film forming condition or the like as described above.
As described above, in the conventional method in which the brush with the varied diameter is used, it is required to prepare various brushes, resulting in a higher cost.
Though it is possible to remove the foreign objects using conventional brushes if the cleaning is performed for a long period of time, a time period of at least about three to four times of a time period required for the cleaning of the wafer with the diameter of about 200 mm is necessary. As a result, a throughput is substantially decreased.
Related arts are disclosed in Patent Document 1 (Japanese Patent Application Laid-open No. 2003-163196) and in Non-patent Document 1(Clean Technology VOL. 8, No. 5 (May 1998)).